Ultrasonic doppler flow meter

Abstract

A flow meter, in which pulsed continuous ultrasonic wave is transmitted towards an object at predetermined intervals T to obtain a phase vector from a reception signal of wave reflected by the object and which calculates a Doppler frequency from the average value of phase differences between phase vectors at the sampling interval T to obtain a signal indicating the speed of the object, comprising a phase difference calculator by the auto-correlation method, by which a plurality of phase difference vectors indicating phase differences between phase vectors are added, the argument of the sum vector thus obtained representing the average phase difference, or a phase difference calculator by the 2-axial-component method, by which a phase difference is divided into 2 axial components, a cosine value and a sine value, and the average phase difference is obtained by using the average value for each of the components, and a phase difference calculator by the phase difference averaging calculator, by which a plurality of phase differences are added, as they are, to obtain the average thereof, in order to obtain a phase difference average value having small errors by switching them.

We claim: 
     
       1. An ultrasonic pulse Doppler flow meter comprising: transmitter-receiver means for transmitting ultrasonic pulsed continuous wave towards an object with a predetermined interval and receiving wave reflected by said object to obtain a reception signal;   phase detecting means for generating a phase vector indicating the phase of said reception signal, each time said reception signal is obtained;   first average phase difference calculating means for obtaining the phase difference Δθ between the phase vector at current time point and the phase vector at the time preceding by one time period, each time said phase vector is obtained, decomposing it into a cosine component and a sine component, and calculating the angle represented by the average of a plurality of cosine components and the average of a plurality of sine components as a first average phase difference;   second average phase difference calculating means for adding said phase difference Δθ a plurality of times to obtain the average thereof as a second average phase difference; and   selecting means for selecting one of said first and said second average phase difference, depending on the magnitude of the speed of said object, as a signal indicating the speed of said object.   
     
     
       2. An ultrasonic pulse Doppler flow meter according to claim 1, wherein said selecting means selects the output of said second average phase difference calculating means when the absolute value of the output of said first average phase difference calculating means is smaller than a predetermined angle and the output of said first average phase difference calculating means when said absolute value is greater than said predetermined angle. 
     
     
       3. An ultrasonic pulse Doppler flow meter according to claim 2, wherein said predetermined angle is in a region comprised between π/3 and π/2. 
     
     
       4. An ultrasonic pulse Doppler flow meter according to claim 1, further comprising means for obtaining successively the speed indicated by said phase difference Δθ to calculate the variation of the speed and means for obtaining the intensity of said reflection signal, said selecting means using said variation of the speed and said intensity of the reflection signal in addition to the output of said first phase difference detecting means as parameters for the selection of the phase difference. 
     
     
       5. An ultrasonic pulse Doppler flow meter according to claim 4, wherein when said variation of the speed exceeds a predetermined value and said intensity of the reflection signal is smaller than a predetermined value, the speed is judged to be impossible to measure or zero. 
     
     
       6. An ultrasonic pulse Doppler flow meter according to claim 1, wherein said selecting means select one of said first and said average phase difference when an average power of said phase vector is larger than a threshold value, and select `zero` when said average power is not larger than said threshold value. 
     
     
       7. An ultrasonic pulse Doppler flow meter comprising: transmitter-receiver means for transmitting ultrasonic pulsed continuous wave towards an object with a predetermined interval and receiving wave reflected by said object to obtain a reception signal;   phase detecting means for generating a phase vector indicating the phase of said reception signal, each time said reception signal is obtained;   first average phase difference calculating means for obtaining the phase difference Δθ between the phase vector at current time point and the phase vector at the time preceding by one time period, each time said phase vector is obtained, decomposing it into a cosine component and a sine component, and calculating the angle represented by the average of a plurality of cosine components and the average of a plurality of sine components as a first average phase difference;   second average phase difference calculating means for adding arguments of said phase difference vector to obtain the average thereof as a second average phase difference; and   selecting means for selecting one of said first and said second average phase difference, depending on the magnitude of the speed of said object, as a signal indicating the speed of said object.   
     
     
       8. An ultrasonic pulse Doppler flow meter according to claim 7, wherein said selecting means selects the output of said second average phase difference calculating means when the absolute value of the output of said first average phase difference calculating means is smaller than a predetermined angle and the output of said first average phase difference calculating means when said absolute value is greater than said predetermined angle. 
     
     
       9. An ultrasonic pulse Doppler flow meter according to claim 8, wherein said predetermined angle is in a region comprised between π/3 and π/2. 
     
     
       10. An ultrasonic pulse Doppler flow meter according to claim 7, further comprising means for obtaining successively the speed indicated by said phase difference Δθ to calculate the variation of the speed and means for obtaining the intensity of said reflection signal, said selecting means using said variation of the speed and said intensity of the reflection signal in addition to the output of said first phase difference detecting means as parameters for the selection of the phase difference. 
     
     
       11. An ultrasonic pulse Doppler flow meter according to claim 10, wherein when said variation of the speed exceeds a predetermined value and said intensity of the reflection signal is smaller than a predetermined value, the speed is judged to be impossible to measure or zero. 
     
     
       12. An ultrasonic pulse Doppler flow meter according to claim 7, wherein said selecting means select one of said first and said average phase difference when an average power of said phase vector is larger than a threshold value, and select `zero` when said average power is not larger than said threshold value. 
     
     
       13. An ultrasonic pulse Doppler flow meter comprising: transmitter-receiver means for transmitting ultrasonic pulsed continuous wave towards an object with a predetermined interval and receiving wave reflected by said object to obtain a reception signal;   phase detecting means for generating a phase vector indicating the phase of said reception signal each time said reception signal is obtained;   first average phase difference calculating means for obtaining the phase difference Δθ between the phase vector at current time point and the phase vector at the time preceding by one time period, each time said phase vector is obtained, decomposing it into a cosine component and a sine component, and calculating the angle represented by the average of a plurality of cosine components and the average of a plurality of sine components as a first average phase difference;   second average phase difference calculating means for adding said phase difference Δθ a plurality of times to obtain the average thereof as a second average phase difference; and   correcting means for correcting said second average phase difference, using said first average phase difference, so that the addition and averaging in said second average phase difference calculating means is substantially effected by using the angle of said first average phase difference as the reference axis for the angle,   wherein the average phase difference corrected by said correcting means is adopted as the signal indicating the speed of said object.   
     
     
       14. An ultrasonic pulse Doppler flow meter according to claim 13, wherein the correction by means of said correcting means is effected, when the absolute value of said first average phase difference exceeds a predetermined threshold value. 
     
     
       15. An ultrasonic pulse Doppler flow meter comprising: transmitter-receiver means for transmitting ultrasonic pulsed continuous wave towards an object with a predetermined interval and receiving wave reflected by said object to obtain a reception signal;   phase detecting means for generating a phase vector indicating the phase of said reception signal, each time said reception signal is obtained;   first average phase difference calculating means for obtaining the phase difference Δθ between the phase vector at current time point and the phase vector at the time preceding by one time period, each time said phase vector is obtained, decomposing it into a cosine component and a sine component, and calculating the angle represented by the average of a plurality of cosine components and the average of a plurality of sine components as a first average phase difference;   second average phase difference calculating means for adding arguments of said phase difference vector to obtain the average thereof as a second average phase difference; and   correcting means for correcting said second average phase difference, using said first average phase difference, so that the addition and averaging in said second average phase difference calculating means is substantially effected by using the angle of said first average phase difference as the reference axis for the angle,   wherein the average phase difference corrected by said correcting means is adopted as the signal indicating the speed of said object.   
     
     
       16. An ultrasonic pulse Doppler flow meter according to claim 15, wherein the correction by means of said correcting means is effected, when the absolute value of said first average phase difference exceeds a predetermined threshold value. 
     
     
       17. An ultrasonic pulse Doppler flow meter comprising: transmitter-receiver means for transmitting ultrasonic pulsed continuous wave towards an object at predetermined intervals T and receiving wave reflected by said object to obtain a reception signal;   phase detecting means for detecting the phase of said reception signal and generating phase vectors sampled at said intervals T;   first auto-correlating means for obtaining a first phase difference vector by correlating phase vectors having said interval T therebetween among said phase vectors sampled at said intervals T to calculate the argument thereof;   second auto-correlating means for obtaining a second phase difference vector by correlating phase vectors having an interval nT (n being an integer not smaller than 2) therebetween among said phase vectors sampled at said intervals T to calculate the argument thereof; and   selecting means for selecting the argument of said first phase difference vector for a high speed region and the argument of said second phase difference vector for a low speed region to obtain a signal indicating the speed of said object.   
     
     
       18. An ultrasonic pulse Doppler flow meter according to claim 17, wherein said selecting means selects the argument of said second phase difference vector when the absolute value of the argument of said first phase difference vector is smaller than a threshold value, which is equal to or slightly smaller than π/n, and the argument of said first phase difference vector when the absolute value of the argument of said first phase difference vector is greater than said threshold value. 
     
     
       19. An ultrasonic pulse Doppler flow meter comprising: transmitter-receiver means for transmitting ultrasonic pulsed continuous wave towards an object at predetermined intervals T and receiving wave reflected by said object to obtain a reception signal;   phase detecting means for detecting the phase of said reception signal and generating phase vectors sampled at said intervals T;   first auto-correlating means for obtaining a first phase difference vector by correlating phase vectors having said interval T therebetween among said phase vectors sampled at said intervals T to calculate the argument thereof;   second auto-correlating means for obtaining a second phase difference vector by correlating phase vectors having an interval nT (n being an integer not smaller than 2) therebetween among said phase vectors sampled at said intervals T to calculate the argument thereof; and   correcting means for judging in which region the argument of said first phase difference vector is among angular regions devided by ±θ L1  and ±θ L2 , wherein θ L1  is π/n and θ L2  is an angle at which spectral characteristics of said first auto-correlation means is a little higher than that of said second auto-correlation means, and effecting corrections on the argument of said second phase difference vector, depending on the judgement result to obtain a signal indicating the speed of said object.